86 CARBONIFEROUS LAMELL1BRANCHIATA. 



M'Coy placed this species witli Inoceramus, but afterwards referred it to 

 Ambonychia, Hall, on account of the discovery of a specimen with a binge, 

 which he describes thus : — "Hinge-line entirely confined to the posterior side 

 of the beak, straight, oblique, with a slender lateral tooth running below 

 its margin for about two-thirds of its length;" and sums up, "It has no 

 relation to the genus Inoceramus on the one hand, nor to Posidonia on the 

 other; but is really a one-eared Avicula of the remarkably thick- shelled genus 

 Ambonychia of Hall." Mr. H. Woods, the Curator of the Woodwardian Museum, 

 informs me that the museum possesses no specimen showing the hinge, and 

 therefore this observation cannot be confirmed. De Koninck points out that 

 M'Coy was in error, as the genus Ambonychia, Hall, "se compose de coquilles munie 

 d'une grande oriellette posterieure, et d'une bord cardinal droit est assez epaise pour 

 porter un certain nombre de dents, qui lui sont paralleles et qui font completement 

 defaut ici. J'ajouterai que la surface de la plupart des Ambonychia est garnie de 

 stries ou de cotes rayonnantes." 



The shell of the species under description is exceedingly thin, and not likely 

 to belong to a genus stated by M'Coy to be remarkably thick- shelled. Phillips 

 thought the shell was inequivalve, and describes the upper valve " flatfish, lower 

 valve very convex ; " but there appears to be no difference in the gibbosity 

 of the valves. De Koninck states that the hinge is edentulous, and this fact 

 will at once separate the shell from Ambonychia. Hall. I have been able 

 to see the specimens on which de Koninck founded his genus Posidoniella, 

 and they are undoubtedly similar to those now figured, but I cannot affirm any 

 statement as to the nature of the anterior part of the hinge. This species 

 can easily be distinguished from all others of the genus by its concentric folds 

 and the convexity of its valves. 



This species has a fairly wide horizontal distribution. Bichwald records it as 

 occurring in the Carboniferous Limestone of Russia. Vertically its range is 

 limited, and I have never found the shell except in pure limestone. 



Posidoniella piriformis, sp. nov., Hind. Plate V, figs. 20, 21, 22; Plate VI, 



figs. 1, 2, 3, 3 a, 4. 



Peena?, Phillips, 1830. Geology of Yorkshire, pi. vi, fig. 14 (no description). 

 Compare Mttilus ajipliatus, de Ryckholt, 1847. Melanges Paleontologiques, pt. 1, p 141, 



pi. viii, figs. 9, 10. 

 — Wesem.eliaxus, de Ryckholt, 1847. Ibid., p. 140, pi. viii, figs. 11, 12. 



Omaliusiaktjs, de Ryckholt, 1847. Ibid., p. 144, pi. viii, figs. 22, 23. 



